1 /* 2 * ladder.c - the residency ladder algorithm 3 * 4 * Copyright (C) 2001, 2002 Andy Grover <andrew.grover@intel.com> 5 * Copyright (C) 2001, 2002 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com> 6 * Copyright (C) 2004, 2005 Dominik Brodowski <linux@brodo.de> 7 * 8 * (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> 9 * Shaohua Li <shaohua.li@intel.com> 10 * Adam Belay <abelay@novell.com> 11 * 12 * This code is licenced under the GPL. 13 */ 14 15 #include <linux/kernel.h> 16 #include <linux/cpuidle.h> 17 #include <linux/pm_qos.h> 18 #include <linux/jiffies.h> 19 #include <linux/tick.h> 20 #include <linux/cpu.h> 21 22 #include <asm/io.h> 23 #include <linux/uaccess.h> 24 25 #define PROMOTION_COUNT 4 26 #define DEMOTION_COUNT 1 27 28 struct ladder_device_state { 29 struct { 30 u32 promotion_count; 31 u32 demotion_count; 32 u32 promotion_time; 33 u32 demotion_time; 34 } threshold; 35 struct { 36 int promotion_count; 37 int demotion_count; 38 } stats; 39 }; 40 41 struct ladder_device { 42 struct ladder_device_state states[CPUIDLE_STATE_MAX]; 43 int last_state_idx; 44 }; 45 46 static DEFINE_PER_CPU(struct ladder_device, ladder_devices); 47 48 /** 49 * ladder_do_selection - prepares private data for a state change 50 * @ldev: the ladder device 51 * @old_idx: the current state index 52 * @new_idx: the new target state index 53 */ 54 static inline void ladder_do_selection(struct ladder_device *ldev, 55 int old_idx, int new_idx) 56 { 57 ldev->states[old_idx].stats.promotion_count = 0; 58 ldev->states[old_idx].stats.demotion_count = 0; 59 ldev->last_state_idx = new_idx; 60 } 61 62 /** 63 * ladder_select_state - selects the next state to enter 64 * @drv: cpuidle driver 65 * @dev: the CPU 66 */ 67 static int ladder_select_state(struct cpuidle_driver *drv, 68 struct cpuidle_device *dev) 69 { 70 struct ladder_device *ldev = this_cpu_ptr(&ladder_devices); 71 struct device *device = get_cpu_device(dev->cpu); 72 struct ladder_device_state *last_state; 73 int last_residency, last_idx = ldev->last_state_idx; 74 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0; 75 int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY); 76 int resume_latency = dev_pm_qos_raw_read_value(device); 77 78 if (resume_latency < latency_req && 79 resume_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) 80 latency_req = resume_latency; 81 82 /* Special case when user has set very strict latency requirement */ 83 if (unlikely(latency_req == 0)) { 84 ladder_do_selection(ldev, last_idx, 0); 85 return 0; 86 } 87 88 last_state = &ldev->states[last_idx]; 89 90 last_residency = cpuidle_get_last_residency(dev) - drv->states[last_idx].exit_latency; 91 92 /* consider promotion */ 93 if (last_idx < drv->state_count - 1 && 94 !drv->states[last_idx + 1].disabled && 95 !dev->states_usage[last_idx + 1].disable && 96 last_residency > last_state->threshold.promotion_time && 97 drv->states[last_idx + 1].exit_latency <= latency_req) { 98 last_state->stats.promotion_count++; 99 last_state->stats.demotion_count = 0; 100 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) { 101 ladder_do_selection(ldev, last_idx, last_idx + 1); 102 return last_idx + 1; 103 } 104 } 105 106 /* consider demotion */ 107 if (last_idx > first_idx && 108 (drv->states[last_idx].disabled || 109 dev->states_usage[last_idx].disable || 110 drv->states[last_idx].exit_latency > latency_req)) { 111 int i; 112 113 for (i = last_idx - 1; i > first_idx; i--) { 114 if (drv->states[i].exit_latency <= latency_req) 115 break; 116 } 117 ladder_do_selection(ldev, last_idx, i); 118 return i; 119 } 120 121 if (last_idx > first_idx && 122 last_residency < last_state->threshold.demotion_time) { 123 last_state->stats.demotion_count++; 124 last_state->stats.promotion_count = 0; 125 if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) { 126 ladder_do_selection(ldev, last_idx, last_idx - 1); 127 return last_idx - 1; 128 } 129 } 130 131 /* otherwise remain at the current state */ 132 return last_idx; 133 } 134 135 /** 136 * ladder_enable_device - setup for the governor 137 * @drv: cpuidle driver 138 * @dev: the CPU 139 */ 140 static int ladder_enable_device(struct cpuidle_driver *drv, 141 struct cpuidle_device *dev) 142 { 143 int i; 144 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0; 145 struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu); 146 struct ladder_device_state *lstate; 147 struct cpuidle_state *state; 148 149 ldev->last_state_idx = first_idx; 150 151 for (i = first_idx; i < drv->state_count; i++) { 152 state = &drv->states[i]; 153 lstate = &ldev->states[i]; 154 155 lstate->stats.promotion_count = 0; 156 lstate->stats.demotion_count = 0; 157 158 lstate->threshold.promotion_count = PROMOTION_COUNT; 159 lstate->threshold.demotion_count = DEMOTION_COUNT; 160 161 if (i < drv->state_count - 1) 162 lstate->threshold.promotion_time = state->exit_latency; 163 if (i > first_idx) 164 lstate->threshold.demotion_time = state->exit_latency; 165 } 166 167 return 0; 168 } 169 170 /** 171 * ladder_reflect - update the correct last_state_idx 172 * @dev: the CPU 173 * @index: the index of actual state entered 174 */ 175 static void ladder_reflect(struct cpuidle_device *dev, int index) 176 { 177 struct ladder_device *ldev = this_cpu_ptr(&ladder_devices); 178 if (index > 0) 179 ldev->last_state_idx = index; 180 } 181 182 static struct cpuidle_governor ladder_governor = { 183 .name = "ladder", 184 .rating = 10, 185 .enable = ladder_enable_device, 186 .select = ladder_select_state, 187 .reflect = ladder_reflect, 188 }; 189 190 /** 191 * init_ladder - initializes the governor 192 */ 193 static int __init init_ladder(void) 194 { 195 /* 196 * When NO_HZ is disabled, or when booting with nohz=off, the ladder 197 * governor is better so give it a higher rating than the menu 198 * governor. 199 */ 200 if (!tick_nohz_enabled) 201 ladder_governor.rating = 25; 202 203 return cpuidle_register_governor(&ladder_governor); 204 } 205 206 postcore_initcall(init_ladder); 207